In general a road paver on a tracked drive runs on a prepared foundation (road bed) onto which a street surface to be produced or road pavement to be produced is to be applied. As a rule the road pavement is a bituminous material, wherein however layers with sand or stone or concrete layers may also be added in. Provided behind the road paver, in the direction of travel, is a height-adjustable screed, and piled on its front side is a supply of the road paving material that is supplied and distributed by a conveyor device that makes sure that the amount of road paving material kept on the front side of the screed is adequate but is not too much. The height of the rear edge of the screed relative to the surface of the prepared foundation, which may also be formed by an old road pavement covering, establishes the thickness of the street surface produced prior to its subsequent further consolidation by rollers. The screed is held on a tow arm that is borne rotatably movable about a tow point arranged in the center area of the road paver, the height of the screed being determined by a hydraulic adjusting device.
FIG. 1 depicts a known road paver as is described for instance in EP 0 542 297 A1. The road paver overall is labeled 10 and includes a tracked drive 12 with which the road paver 10 travels on the prepared foundation 14. Arranged on the back end of the road paver 10, as seen in the direction of travel, is a height-adjustable screed 16 that is linked to the road paver 10 at a tow point 20 by means of a tow arm 18. Disposed in front of the screed 16 is a supply 22 of the asphalt material, this supply being kept constant essentially across the entire width of the screed 16 using corresponding control, known per se, of the speed of a screw-like conveyor device 24. The screed 16 floats on the asphalt of the road surface to be produced. The thickness of the road surface to be produced prior to its final consolidation by road rollers is adjusted by adjusting the height of the rear edge 26 of the screed 16. This height adjustment is initiated by changing the setting angle of the screed 16, and is typically accomplished by actuating adjusting cylinders that engage at the front ends of the tow arms 18. The road paver includes three ultrasound sensors 28, 30, 32 that are attached to a mount 34. The mount 34 is attached to the tow arm 18. The three ultrasound sensors 28, 30, 32 scan a reference surface that may be formed for instance by an old path of the road cover or by a path of the road cover that has already been produced.
When building a road, it is desirable to measure the produced layer as continuously and in real time as possible. Determining the layer thickness is desired for instance to check the quality of the newly applied road pavement. If the calculated thickness of, for instance, a bituminous layer is too low, there is the risk that the road pavement will break up prematurely, which results in expensive repairs to the road pavement. On the other hand, the layer thickness may be checked with respect to the quantity of material used so that the quantity of material used is not too high, which would lead to increased costs.
Known systems for determining the layer thickness of newly applied road pavement are described for instance in EP 2 535 456 A1, EP 2 535 457 A1, and EP 2 535 458 A1. It is a drawback of these known systems that they are mechanically complex and complicated in terms of signal processing and yet still do not have adequate accuracy when determining the layer thickness.
U.S. Pat. No. 7,172,363 B2 describes a road paver having a sensor frame which comprises lateral height sensors, front height sensors in front of the screed and rear height sensors behind the screed, each of which measures the distance from the foundation. The sensor frame is rigidly attached to the screed and/or to the tow arm.